dt-bindings: power: supply: summit,smb347: Add missing power-supply ref

Reference the common power supply schema to bring the definition of
monitored-battery property.  Drop also the obvious description because
it is duplicating what is in power-supply.yaml.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: David Heidelberg <david@ixit.cz>
Link: https://lore.kernel.org/r/20250604-dt-bindings-psy-monitored-battery-v1-5-7f755ff75218@linaro.org
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Documentation/devicetree/bindings/power/supply/summit,smb347-charger.yaml

@@ -23,9 +23,7 @@ properties:
   interrupts:
     maxItems: 1
 
-  monitored-battery:
-    description: phandle to the battery node
-    $ref: /schemas/types.yaml#/definitions/phandle
+  monitored-battery: true
 
   summit,enable-usb-charging:
     type: boolean
@@ -94,6 +92,7 @@ properties:
     unevaluatedProperties: false
 
 allOf:
+  - $ref: power-supply.yaml#
   - if:
       properties:
         compatible: